Development of the earthworm Pontoscolex corethrurus in soils amended with a peat-based plant growing medium

An experiment was set in laboratory conditions to determine the capacity of Pontoscolex corethrurus to develop in a substrate rich in organic matter and to define the percentage of organic matter where development was best as it is an endogeic geophagous earthworm that typically occurs in mineral-rich rather than organically rich soils. Five treatments were established in soil (S) as the control and then this soil was enriched with 25% (S25), 50% (S50), 75% (S75) and 100% (OM) of a commercial substrate composed mainly of peat moss (Sphagnum). The physico-chemical parameters of the mixed substrates and cast were determined. The growth of the earthworms was measured every 15 days during 90 days, as well as cocoon and cast production and mortality. The results show that P. corethrurus is unable to grow in a substrate of 75 to a 100% organic matter where its mortality was seen to be more than 56-100%. Its optimal development was in S and in S25 reaching an individual weight of 0.6 g and a cocoon production of 44 ind.−1 y−1. Its substrate consumption was shown to be less when the soil was richer in organic matter and the cast production varied from 0.33 to 0.047 g ind.−1 per day−1. From a comparison of the composition of substrates and cast physico-chemical parameters, we observed that P. corethrurus chooses its food, concentrating on organic matter but breaks down fibers of Sphagnum, particularly hemicellulose fibers by up to 17%.